1. Field of the Invention
This invention is directed to peptides that antagonize insulin-like growth factor (IGF), in particular, IGF-1. These peptides are useful in treating disorders caused or mediated by IGFs, such as cancer.
2. Description of Related Disclosures
There is a large body of literature on the actions and activities of IGFs (IGF-1, IGF-2, and IGF variants). Human IGF-1 is a 7649-dalton polypeptide with a pI of 8.4 (Rinderknecht and Humbel, Proc. Natl. Acad. Sci. USA, 73: 2365 (1976); Rinderknecht and Humbel, J. Biol. Chem., 253: 2769 (1978)) belonging to a family of somatomedins with insulin-like and mitogenic biological activities that modulate the action of growth hormone (GH) (Van Wyk et al., Recent Prog. Horm. Res., 30: 259 (1974); Binoux, Ann. Endocrinol., 41: 157 (1980); Clemmons and Van Wyk, Handbook Exp. Pharmacol., 57: 161 (1981); Baxter, Adv. Clin. Chem., 25:49 (1986); U.S. Pat. No. 4,988,675; WO 91/03253; WO 93/23071). IGFs are structurally similar to insulin, and have been implicated as a therapeutic tool in a variety of diseases and injuries.
The IGF system is also composed of membrane-bound receptors for IGF-1, IGF-2, and insulin. The Type 1 IGF receptor (IGF-1R) is closely related to the insulin receptor in structure and shares some of its signaling pathways (Jones and Clemmons, Endocr. Rev., 16: 3-34 (1995)). The IGF-2 receptor is a clearance receptor that appears not to transmit an intracellular signal (Jones and Clemmons, supra). Since IGF-1 and IGF-2 bind to IGF-1R with a much higher affinity than to the insulin receptor, it is most likely that most of the effects of IGF-1 and IGF-2 are mediated by IGF-1R (Humbel, Eur. J. Biochem. 190:445-462 (1990); Ballard et al., “Does IGF-I ever act through the insulin receptor?”, in Baxter et al. (Eds.), The Insulin-Like Growth Factors and Their Regulatory Proteins, (Amsterdam: Elsevier, 1994), pp. 131-138). The crystal structure of the first three domains of IGF-1R has been determined (Garrett et al., Nature, 394, 395-399 (1998)).
IGF-1R is a key factor in normal cell growth and development (Daughaday and Rotwein, Endocrine Rev., 10:68-91 (1989)). Increasing evidence suggests, however, that IGF-1R signaling also plays a critical role in growth of tumor cells, cell transformation, and tumorigenesis (Baserga, Cancer Res., 55:249-252 (1995); for a review, see Khandwala et al., Endocr. Rev. 21: 215-244 (2000)). Key examples include loss of metastatic phenotype of murine carcinoma cells by treatment with antisense RNA to the IGF-1R (Long et al., Cancer Res., 55:1006-1009 (1995)) and the in vitro inhibition of human melanoma cell motility (Stracke et al., J. Biol. Chem., 264:21554-21559 (1989)) and of human breast cancer cell growth by the addition of IGF-1R antibodies (Rohlik et al., Biochem. Biophys. Res. Commun., 149:276-281 (1987)).
The IGFs are potent breast cancer cell mitogens based on the observation that IGF-1 enhanced breast cancer cell proliferation in vitro (Cullen et al., Cancer Res., 50:48-53 (1990)). Breast cancers express IGF-2 and IGF-1R, providing all the required effectors for an autocrine-loop-based proliferation paradigm (Quinn et al., J. Biol. Chem., 271:11477-11483 (1996); Steller et al., Cancer Res., 56:1761-1765 (1996)). Because breast cancer is a common malignancy affecting approximately one in every eight women and is a leading cause of death from cancer in North American women (LeRoith et al., Ann. Int. Med., 122:54-59 (1995)), new rational therapies are required for intervention. IGF-1 can suppress apoptosis, and therefore cells lacking IGF-1Rs or having compromised IGF-1R signaling pathways may give rise to tumor cells that selectively die via apoptosis (Long et al., Cancer Res., 55:1006-1009 (1995)). Furthermore, it has recently become evident that alterations in IGF signaling in the context of other disease states, such as diabetes, may be responsible for exacerbating the complications of retinopathy (Smith et al., Science, 276:1706-1709 (1997)) and nephropathy (Homey et al., Am. J. Physiol. 274: F1045-F1053 (1998)).
The IGF binding proteins (IGFBPs) are a family of at least six proteins (Jones and Clemmons, supra; Bach and Rechler, Diabetes Reviews, 3: 38-61 (1995)), that modulate access of the IGFs to the IGF-1R. They also regulate the concentrations of IGF-1 and IGF-2 in the circulation and at the level of the tissue IGF-1R (Clemmons et al., Anal. NY Acad. Sci. USA, 692:10-21 (1993)). The IGFBPs bind IGF-1 and IGF-2 with varying affinities and specificities (Jones and Clemmons, supra; Bach and Rechler, supra). For example, IGFBP-3 binds IGF-1 and IGF-2 with a similar affinity, whereas IGFBP-2 and IGFBP-6 bind IGF-2 with a much higher affinity than they bind IGF-1 (Bach and Rechler, supra; Oh et al., Endocrinology, 132, 1337-1344 (1993)).
In most cases, addition of exogenous IGFBP blunts the effects of IGF-1. For example, the growth-stimulating effect of estradiol on the MCF-7 human breast cancer cells is associated with decreased IGFBP-3 mRNA and protein accumulation, while the anti-estrogen ICI 182780 causes growth inhibition and increased IGFBP-3 mRNA and protein levels (Huynh et al., J. Biol. Chem., 271:1016-1021 (1996); Oh et al., Prog. Growth Factor Res., 6:503-512 (1995)). It has also been reported that the in vitro inhibition of breast cancer cell proliferation by retinoic acid may involve altered IGFBP secretion by tumor cells or decreased circulating IGF-1 levels in vivo (LeRoith et al., Ann. Int. Med., 122:54-59 (1995); Oh et al., (1995), supra). Contrary to this finding, treatment of MCF-7 cells with the anti-estrogen tamoxifen decreases IGF-1R signaling in a manner that is unrelated to decreased IGFBP production (Lee et al., J. Endocrinol., 152:39 (1997)). Additional support for the general anti-proliferative effects of the IGFBPs is the striking finding that IGFBP-3 is a target gene of the tumor suppressor, p53 (Buckbinder et al., Nature, 377:646-649 (1995)). This suggests that the suppressor activity of p53 is, in part, mediated by IGFBP-3 production and the consequential blockade of IGF action (Buckbinder et al., supra). These results indicate that the IGFBPs can block cell proliferation by modulating paracrine/autocrine processes regulated by IGF-1/IGF-2. A corollary to these observations is the finding that prostate-specific antigen (PSA) is an IGFBP-3-protease, which upon activation, increases the sensitivity of tumor cells to the actions of IGF-1/IGF-2 due to the proteolytic inactivation of IGFBP-3 (Cohen et al., J. Endocr., 142:407-415 (1994)). The IGFBPs complex with IGF-1/IGF-2 and interfere with the access of IGF-1/IGF-2 to IGF-1Rs (Clemmons et al., Anal. NY Acad. Sci. USA, 692:10-21 (1993)). IGFBP-1, -2 and -3 inhibit cell growth following addition to cells in vitro (Lee et al. , J Endocrinol., 152:39 (1997); Feyen et al., J Biol. Chem., 266:19469-19474 (1991)). Further, IGFBP-1 (McGuire et al., J Natl. Cancer Inst., 84:1335-1341(1992); Figueroa et al., J Cell Physiol., 157:229-236 (1993)), IGFBP-3 (Oh et al. (1995), supra; Pratt and Pollak, Biophys. Res. Commun., 198:292-297 (1994)) and IGFBP-2 have all been shown to inhibit IGF-1 or estrogen-induced breast cancer cell proliferation at nanomolar concentrations in vitro. These findings support the idea that the IGFBPs are potent antagonists of IGF action. There is also evidence for a direct effect of IGFBP-3 on cells through its own cell surface receptor, independent of IGF interactions (Oh et al, J Biol. Chem., 268:14964-14971 (1993); Valentinis et al., Mol. Endocrinol., 9:361-367 (1995)). Taken together, these findings underscore the importance of IGF and IGF-1R as targets for therapeutic use.
Unlike most other growth factors, the IGFs are present in high concentrations in the circulation, but only a small fraction of the IGFs is not protein bound. For example, it is generally known that in humans or rodents, less than 1% of the IGFs in blood is in a “free” or unbound form (Juul et al., Clin. Endocrinol., 44: 515-523 (1996); Hizuka et al., Growth Regulation, 1: 51-55 (1991); Hasegawa et al., J. Clin. Endocrinol. Metab., 80: 3284-3286 (1995)). The overwhelming majority of the IGFs in blood circulate as part of a non-covalently associated ternary complex composed of IGF-1 or IGF-2, IGFBP-3, and a large protein termed the acid-labile subunit (ALS). This complex is composed of equimolar amounts of each of the three components. The ternary complex of an IGF, IGFBP-3, and ALS has a molecular weight of approximately 150,000 daltons, and it has been suggested that the function of this complex in the circulation may be to serve as a reservoir and buffer for IGF-1 and IGF-2, preventing rapid changes in free IGF-1 or IGF-2.
Maintaining normal levels of IGF-1 signaling are important for proper cellular function, since both down-and up-regulation of IGF-1-related pathways have been implicated in several human diseases. The rate of cell proliferation is positively correlated with risk of transformation of certain epithelial cell types (Cohen and Ellwein, Science, 249:1007 (1990); Cohen and Ellwein, Cancer Research 51:6493 (1991)). Relatively high plasma IGF-1 and low IGF binding protein-3 levels are associated with greater risk of breast cancer in pre-menopausal women, prostate cancer in men, colorectal cancer in men and women, and lung cancer in men and women; additional in vitro and in vivo studies reflecting a link between IGF and cancer are found in “Insulin-Like Growth Factors and Cancer”, Cytokine Bulletin, R&D Systems (Fall 2000 edition), pages 2-3. IGFs have mitogenic and anti-apoptotic influences on normal and transformed prostate epithelial cells (Hsing et al., Cancer Research, 56: 5146 (1996); Culig et al., Cancer Research, 54: 5474 (1994); Cohen et al., Hormone and Metabolic Research, 26: 81 (1994); Iwamura et al., Prostate, 22: 243 (1993); Cohen et al., J. Clin. Endocrin. & Metabol., 73: 401 (1991); Rajah et al., J. Biol. Chem., 272: 12181 (1997)). Most circulating IGF-1 originates in the liver, but IGF bioactivity in tissues is related not only to levels of circulating IGFs and IGFBPs, but also to local production of IGFs, IGFBPs, and IGFBP proteases (Jones and Clemmons, Endocrine Reviews, 16: 3 (1995)). Person-to-person variability in levels of circulating IGF-1 and IGFBP-3 (the major circulating IGFBP (Jones and Clemmons, supra)) is considerable (Juul et al., J. Clin. Endocrinol. & Metabol., 78: 744 (1994); Juul et al, J. Clin. Endocrinol. & Metabol., 80: 2534 (1995)), and heterogeneity in serum IGF-1 level appears to reflect heterogeneity in tissue IGF bioactivity. Markers relating to IGF-axis components can be used as a risk marker for prostate cancer, as PSA is likewise used (WO 99/38011). Further, it has been found that reduced IGF-1 concentrations in serum correlate with improved clinical scores in acromegaly patients (Trainer et al., New England J. Med., 342: 1171-1177 (2000)).
There has been much work identifying the regions on IGF-1 and IGF-2 that bind to the IGFBPs (Bayne et al., J. Biol. Chem., 265: 15648-15652 (1990); Dubaquie and Lowman, Biochemistry, 38: 6386-6396 (1999); and U.S. Pat. Nos. 5,077,276; 5,164,370; and 5,470,828). For example, it has been discovered that the N-terminal region of IGF-1 and IGF-2 is critical for binding to the IGFBPs (U.S. Pat. Nos. 5,077,276; 5,164,370; and 5,470,828). Thus, the natural IGF-1 variant, designated des (1-3) IGF-1, binds poorly to IGFBPs.
A similar amount of research has been devoted to identifying the regions on IGF-1 and IGF-2 that bind to IGF-1R (Bayne et al., supra; Oh et al., Endocrinology (1993), supra). It was found that the tyrosine residues in IGF-1 at positions 24, 31, and 60 are crucial to the binding of IGF-1 to IGF-1R (Bayne et al., supra). Mutant IGF-1 molecules where one or more of these tyrosine residues are substituted showed progressively reduced binding to IGF-1R. Bayne et al., supra, also investigated whether such mutants of IGF-1 could bind to IGF-1R and to the IGFBPs. They found that quite different residues on IGF-1 and IGF-2 are used to bind to the IGFBPs from those used to bind to IGF-1R. It is therefore possible to produce IGF variants that show reduced binding to the IGFBPs, but, because they bind well to IGF-1R, show maintained activity in in vitro activity assays.
Also reported was an IGF variant that binds to IGFBPs but not to IGF receptors and therefore shows reduced activity in in vitro activity assays (Bar et al., Endocrinology, 127: 3243-3245 (1990)). In this variant, designated (1-27, gly4, 38-70)-hIGF-1, residues 28-37 of the C region of human IGF-1 are replaced by a four-residue glycine bridge.
Other truncated IGF-1 variants are disclosed. For example, in the patent literature, WO 96/33216 describes a truncated variant having residues 1-69 of authentic IGF-1. EP 742,228 discloses two-chain IGF-1 superagonists, which are derivatives of the naturally occurring, single-chain IGF-1 having an abbreviated C region. The IGF-1 analogs are of the formula: BCn,A
wherein B is the B region of IGF-1 or a functional analog thereof, C is the C region of IGF-1 or a functional analog thereof, n is the number of amino acids in the C region and is from about 6 to about 12, and A is the A region of IGF-1 or a functional analog thereof.
Additionally, Cascieri et al., Biochemistry, 27: 3229-3233 (1988) discloses four mutants of IGF-1, three of which have reduced affinity to IGF-1R. These mutants are: (Phe23,Phe24,Tyr25)IGF-1 (which is equipotent to human IGF-1 in its affinity to the Types 1 and 2 IGF and insulin receptors), (Leu24)IGF-I and (Ser24)IGF-1 (which have a lower affinity than IGF-1 to the human placental IGF-1R, the placental insulin receptor, and the IGF-1R of rat and mouse cells), and desoctapeptide (Leu24)IGF-1 (in which the loss of aromaticity at position 24 is combined with the deletion of the carboxyl-terminal D region of hIGF-1, which has lower affinity than (Leu 24)IGF-1 for the IGF-1R and higher affinity for the insulin receptor). These four mutants have normal affinities for human serum binding proteins.
Bayne et al., J. Biol. Chem., 263: 6233-6239 (1988) discloses four structural analogs of human IGF-1: a B-chain mutant in which the first 16 amino acids of IGF-1 were replaced with the first 17 amino acids of the B-chain of insulin, (Gln3,Ala4)IGF-1, (Tyr15,Leu16)IGF-1, and (Gln3,Ala4,Tyr15,Leu16)IGF-1. These studies identify some of the regions of IGF-1 that are responsible for maintaining high-affinity binding with the serum binding protein and the Type 2 IGF receptor.
In another study, Bayne et al., J. Biol. Chem., 264: 11004-11008 (1988) discloses three structural analogs of IGF-1: (1-62)IGF-1, which lacks the carboxyl-terminal 8-amino-acid D region of IGF-1; (1-27,Gly4, 38-70)IGF-1, in which residues 28-37 of the C region of IGF-1 are replaced by a four-residue glycine bridge; and (1-27,Gly4, 38-62)IGF-1, with a C region glycine replacement and a D region deletion. Peterkofsky et al., Endocrinology, 128: 1769-1779 (1991) discloses data using the Gly4 mutant of Bayne et al., supra (vol. 264).
Cascieri et al., J. Biol. Chem., 264: 2199-2202 (1989) discloses three IGF-1 analogs in which specific residues in the A region of IGF-1 are replaced with the corresponding residues in the A chain of insulin. The analogs are: (Ile41,Glu45,Gln46,Thr49,Ser50,Ile51,Ser53,Tyr55,Gln56)IGF-1, an A-chain mutant in which residue 41 is changed from threonine to isoleucine and residues 42-56 of the A region are replaced; (Thr49,Ser50,Ile51)IGF-1; and (Tyr55,Gln56)IGF-1.
Clemmons et al., J. Biol. Chem., 265: 12210-12216 (1990) discloses use of IGF-1 analogs that have reduced binding affinity for either IGF-1R or binding proteins to study the ligand specificity of IGFBP-1 and the role of IGFBP-1 in modulating the biological activity of IGF-1.
WO 94/04569 discloses a specific binding molecule, other than a natural IGFBP, that is capable of binding to IGF-1 and can enhance the biological activity of IGF-1.
The direction of research into IGF variants has mostly been to make IGF variants that do not bind to the IGFBPs, but show maintained binding to the IGF receptor. The idea behind the study of such molecules is that the major actions of the IGFBPs are proposed to be an inhibition of the activity of the IGFs. Chief among these variants is the natural molecule, des(1-3)IGF-1, which shows selectively reduced affinity for some of the IGF binding proteins, yet a maintained affinity for the IGF receptor (U.S. Pat. Nos. 5,077,276; 5,164,370; 5,470,828).
Peptides that bind to IGFBP-1, block IGF-1 binding to this binding protein, and thereby release “free-IGF” activity from mixtures of IGF-1 and IGFBP-1 have been recently described (Lowman et al., Biochemistry, 37: 8870-8878 (1998); WO 98/45427 published Oct. 15, 1998; Lowman et al., International Pediatric Nephrology Association, Fifth Symposium on Growth and Development in Children with Chronic Renal Failure (New York, Mar. 13, 1999)).
Exploitation of the interaction between IGF and IGFBP in screening, preventing, or treating disease has been limited, however, because of a lack of specific antagonists. To date, only one publication is known to exist that describes the application of an IGF-1/IGF-2 antagonist as a potential therapeutic adjunct in the treatment of cancer (Pietrzkowski et al., Cancer Res., 52: 6447-6451 (1992)). In that report, a peptide corresponding to the D-region of IGF- I was synthesized for use as an IGF-½ antagonist. This peptide exhibited questionable inhibitory activity against IGF-1. The basis for the observed inhibition is unclear as the D-region does not play a significant role in IGF- IR binding but rather, in IGF-1 binding to the insulin receptor (Cooke et al., Biochem., 30:5484-5491 (1991); Bayne et al., J Biol. Chem. 264:11004-11008 (1988); Yee et al., Cell Growth and Different., 5:73-77 (1994)). IGF antagonists whose mechanism of action is via blockade of interactions at the IGF-1R interface may also significantly alter insulin action at the insulin receptor, a disadvantage of such antagonists.
Recently, certain IGF-1 antagonists have been described by WO 00/23469, which discloses the portions of IGFBP and IGF peptides that account for IGF-IGFBP binding, i.e., an isolated IGF binding domain of an IGFBP or modification thereof that binds IGF with at least about the same binding affinity as the full-length IGFBP. The patent publication also discloses an IGF antagonist that reduces binding of IGF to an IGF receptor, and/or binds to a binding domain of IGFBP. Disclosed uses of such antagonists and fragments are in treating a subject having cancer and preventing cancer in a subject, treating a subject with a diabetic complication exacerbated by IGF and preventing diabetic complications exacerbated by IGF, or treating a subject with an ischemic injury or preventing an ischemic injury in a subject.
Additionally, EP 639981 discloses pharmaceutical compositions comprising short peptides that function as IGF-1 receptor antagonists. The peptides used in the pharmaceutical compositions consist of less than 25 amino acids, comprise at least a portion of the C or D region from IGF-1, and inhibit IGF-1-induced autophosphorylation of IGF-1 receptors. Methods of inhibiting cell proliferation and of treating individuals suspected of suffering from or susceptible to diseases associated with undesirable cell proliferation such as cancer, restenosis and asthma are disclosed.
Generation of specific IGF-1 antagonists has been restricted, at least in part, because of difficulties in studying the structure of IGF and IGFBP. Due to the inability to obtain crystals of IGF-1 suitable for diffraction studies, for example, an extrapolation of IGF-1 structure based on the crystal structure of porcine insulin was the most important structural road map for IGF-1 available (Blundell et al. , Proc. Natl. Acad. Sci. USA, 75:180-184 (1978)). See also Blundell et al., Fed. Proc. 42: 2592 (1983), which discloses tertiary structures, receptor binding, and antigenicity of IGFs. Based on studies of chemically modified and mutated IGF-1, a number of common residues between IGF-I and insulin have been identified as being part of the IGF-1R-insulin receptor contact site, in particular the aromatic residues at positions 23-25. Using NMR and restrained molecular dynamics, the solution structure of IGF-1 was recently reported (Cooke et al., supra). The resulting minimized structure was shown to better fit the experimental findings on modified IGF-1, as well as the extrapolations made from the structure-activity studies of insulin. Further, De Wolf et al., Protein Sci., 5: 2193 (1996) discloses the solution structure of a mini-IGF-1. Sato et al., Int. J. Pept., 41: 433 (1993) discloses the three-dimensional structure of IGF-1 determined by 1H-NMR and distance geometry. Torres et al., J Mol Biol. 248: 385 (1995) discloses the solution structure of human IGF-2 and its relationship to receptor and binding protein interactions. Laajoki et al., J. Biol. Chem., 275: 10009 (2000) discloses the solution structure and backbone dynamics of long-[Arg(3)]IGF-1.
Peptide sequences capable of binding to insulin and/or insulin-like growth factor receptors with either agonist or antagonist activity and identified from various peptide libraries are described in WO 01/72771 published Oct. 4, 2001.
There is a continuing need in the art for a molecule that acts as an IGF antagonist to control the levels of circulating IGF as well as receptor response, for therapeutic or diagnostic purposes.